Virtual private network (VPN) routing and forwarding (referred to herein as VRF) has been used widely in data networks. There are many reasons for its popularity, including security, traffic engineering, and quality of service. A VRF site may utilize a routing and forwarding table associated with one or more directly connected VPN sites (such as customer edge routers and provider edge routers). This VRF table can also contain routes for other VPN sites not directly connected to the VRF site. Many platforms support VRF combined with multiprotocol labeled switching (MPLS) and/or VPN for data traffic.
The use of voice over Internet Protocol (VoIP) has gained momentum in the past several years and is increasing dramatically in both enterprise networks and service provider networks. However, in current VoIP solutions, call routing is handled by resolving a remote IP address, which doesn't satisfy VRF's routing requirement that a specified VRF label must be associated with a VRF route. Currently, there is no mechanism that provides efficient VoIP call routing over the current VRF environment.
Current VoIP standards, including H.323, session initiation protocol (SIP), media gateway control protocol (MGCP) and skinny client control protocol (SCCP), are completely unaware of the VRF routing. VoIP call routing by the existing VoIP protocols gives the remote IP addresses for both signaling and media, but it doesn't understand nor take advantage of the underlying VRF routing capability.
One approach to solving this problem is to use access control lists and virtual interfaces in local gateways to classify some VoIP calls into different VRF routes. This approach suffers several drawbacks. Access control lists and virtual interfaces fail if call routing is controlled by a central agent (such as gatekeeper, SIP proxy, or call agent), and don't provide necessary control on per-call VoIP routing. This approach also suffers scalability problems when more VRF routes are introduced.
Thus, there is a heartfelt need for an intelligent control mechanism for delivering VoIP call signaling traffic as well as VoIP media traffic through a desired VRF path. Also needed are intelligent controls such as bandwidth management and call admission control over shared VRF routes among all VoIP calls in a VRF environment, especially for H.323 zones controlled by a gatekeeper, SIP domains controlled by SIP proxy servers, and MGCP environments controlled by call agents.